Odd-even effects in the threshold and saturation behaviour of long pitch cholesteric systems

The cholesteric-nematic phase change under tilted surface alignment has been investigated in long pitch systems. An alternation of the saturation voltage with increasing ratio between cell thickness and helical pitch and an alternation in the relaxation behaviour have been observed. The internal structure of tilted cholesteric systems is useful to discuss these results.     

Capillary electrophoretic resolution of the enantiomers of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, the key flavor compounds in strawberry fruit

Summary A simple capillary electrophoretic method with UV detection has been developed for resolution of the enantiomers of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, the key flavor compounds in strawberry fruit. The separation was performed in fused-silica capillaries (30/40.2 cm long×50μm i.d.) with running buffer consisting of 50mm ammonium acetate, pH 4.0, containing 20mm heptakis-(2,3-O-diacetyl-6-O-sulfato)-β-cyclodextrin (HDAS-β CD). The applied potential was 10 kV, the temperature 25°C, and detection was at 280 nm. The method was used to determine the enantiomer ratio of 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) isolated from strawberry fruits and from the yeastZygosaccharomyces rouxii. The formation of enantiomerically enriched(+)-DMHF byZ. rouxii was demonstrated for, the first time.     

Metallkomplexe mit biologisch wichtigen Liganden. CLXV N,O‐Chelat‐Komplexe von α‐Aminosäureanionen mit cyclopalladiertem N,N‐Dimethylferrocencarbothiamid

Metal Complexes of Biologically Important Ligands. CLXV N,O‐Chelate Complexes of α‐Amino Acid Anions with Cyclopalladated N,N‐Dimethylferrocenecarbothioamide A short literature review on the reactions of various chlorobridged complexes with α‐aminoacidates, α‐amino acid esters, peptide ester or derivatives of amino acids is given. The chloro bridged o‐palladated N,N‐dimethylferrocenecarbothioamide [(fct)Pd(μ‐Cl)₂Pd(fct)] reacts with the anions of glycine, L‐alanine, L‐proline, L‐valine, L‐phenylalanine, L‐leucine, L‐isoleucine to give the N,O‐chelates [(fct)Pd(N,O‐α‐aminocarboxylate)] ( 1 – 7 ). Due to the planary chirality of the unsymmetrically disubstituted cyclopentadienyl iron moiety of fct the complexes 2 – 7 with optically active amino acidate ligands are formed as a mixture of two diastereoisomers, which can be detected by their NMR spectra.     

An efficient one-pot synthesis of coumarin-amino acid derivatives as potential anti-inflammatory and antioxidant agents

Abstract

A series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (¹H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard.     

Influence of Additives and Surface Topography on the Alignment of Nematic Liquid Crystals

Observations of the influence of a simultaneous action of different surface topographies and polar or nonpolar additives in small concentration on the alignment properties of liquid crystal molecules are reported. The additive dependence of the threshold behaviour of planar aligned liquid crystal cells is also studied.     

Helical structure and threshold voltage of cholesteric-nematic phase change at different anchoring conditions

The helical structure of cholesteric mixed systems and their electro-optical behaviour are studied at planar and pretilted surface orientation. The results indicate that the influence of the forces of wall orientation is decreased by the helical structure. To prove this model strong and weak anchoring conditions of the molecules in the cholesteric mixture at the substrate surface are realized. Also the behaviour of the electro-optical threshold voltage at different surface conditions supports the assumptions concerning the helical structure.